a. Field of the Invention
The present disclosure relates to medical devices in general, and to methods and systems for producing an electrophysiological map, in particular.
b. Background Art
Cardiac arrhythmia is a well known medical condition where the regular beating rhythm of the heart is disrupted. These disruptions are caused by disturbances in the propagation path of electrical impulses in the myocardial tissue. These disturbances are caused, for example, by ischemia to a region in the myocardial tissue. Thus, the propagation of electrical impulses, through the myocardial tissue, may slow down. These ischemic regions create patterns of circular propagation of electric impulses. This circular propagation pattern disrupts the normal propagation pattern of electrical impulse, thus, causing irregular activation of the atria or ventricle. As a further example, cardiac arrhythmias are also caused by anatomical obstacles (e.g., dead tissue). These obstacles cause electric impulses to propagate around the obstacles, thus, disrupting the normal propagation of impulses to the atria or ventricular.
These conditions may be treated with an ablation procedure. During this procedure, a physician inserts an ablation catheter to the region of interest where abnormal propagation of electric impulses occurs, and ablates that region. This ablation is performed by using, for example, heat, electromagnetic pulses or cryogenic fluid.
Abnormal propagation pathways are found by an electrophysiology study procedure of the heart. During this procedure, a physician typically inserts an electrode or electrodes into or near the heart. During the arrhythmia electrodes measure the electric potential at different locations in the heart. Using this information, an electric potential map of the heart is formed, identifying regions of interest.
U.S. Patent Application Publication No. 2003/0158477 to Panescu and entitled “Systems and Methods for Guiding Catheters Using Registered Images”, is directed to a system for producing a three-dimensional volume of the heart. The system includes a mapping catheter, a registration processor, a plurality of fiducials, and an external imaging device. The mapping catheter includes a plurality of mapping elements at its tip. The fiducials are attached to the chest of the patient. The fiducials which show up on an image of the heart, can be used to register an externally acquired image with a three-dimensional coordinate system.
U.S. Pat. No. 5,595,183 to Swanson et al., entitled “Systems and Methods for Examining Heart Tissue Employing Multiple Electrode Structures and Roving Electrodes” (Swanson et al. '183), is directed to a system and a method for pacing and mapping the heart for the diagnosis and treatment of cardiac conditions. Swanson et al. '183 is directed to a system including a mapping probe and an ablation probe. The mapping probe carries a three dimensional multiple electrode structure which takes the form of a basket. This basket structure is formed by splines extending from a base member (i.e., where the splines are connected to the catheter) to an end cap (i.e., where the splines are connected together). These splines are made from Nitinol metal or silicone rubber. A plurality of electrodes, are positioned on each of these splines. These electrodes are operative as either sensors or sources of electrical energy at the point of contact with the myocardial tissue.
The Swanson system operates in two modes, the sampling mode and the matching mode. In the sampling mode, the basket structure is deployed in the desired region of the heart. An electrode or pairs of electrodes are activated to produce electrical energy to the myocardial tissue pacing the heart. The electrodes then record electrograms. In the matching mode, the system compares the resulting paced electrogram morphologies to a plurality of electrogram morphology templates collected during the sampling mode. Based upon this comparison, the system generates an output that identifies the location of an electrode or electrodes on the basket structure that are close to a possible ablation site. An ablation catheter is then inserted for ablating the site.
U.S. Pat. No. 5,876,336 to Swanson et al., entitled “Systems and Methods for Guiding Movable Electrode Elements Within Multiple Electrode Structure” (Swanson et al. '336), is directed to a method and a system for remotely locating electrode elements at precise locations within the body of a patient. The system in Swanson et al. '336 includes a mapping probe and an ablation probe. The mapping probe carries a three dimensional multiple electrode structure which takes the form of a basket. This basket structure is formed by splines extending from a base member to an end cap. These splines are made from Nitinol metal or silicone rubber. A plurality of electrodes is positioned on each of these splines. These electrodes sense electrical activity in heart tissue. The sensed electrical activity is processed to create a map of this electrical activity. A physician uses this map to identify regions for possible ablation.
Once a region is selected for ablation, an ablation probe (i.e., ablation catheter), including an ablation electrode, is inserted to the heart and placed in contact with the tissue in the selected region. The ablation electrode emits ablation energy (e.g., heat or electromagnetic energy) to the contacted heart tissue to destroy that tissue.
The '336 system includes a processing unit for guiding the ablation catheter. This processing unit determines the position of the ablation catheter within the space defined by the basket structure in terms of the relative position of the electrodes on the basket splines. First, the position of the ablation of the catheter in a horizontal sector, between adjacent horizontal sets of electrodes is determined. This horizontal sector is determined by sensing the phase difference between the phase of an oscillator signal, sequentially applied to each set of electrodes and the phase of the ablation electrode. If the ablation catheter is beneath the electrode set, the phase difference sign is negative. If the ablation catheter is above the electrode set, the phase difference sign is positive.
Next, an arcuate sector symmetrically bisected by a spline is determined. This arcuate sector is determined using differential amplitude sensing or differential phase sensing between the ablation electrode and a spline, to which an oscillating signal is applied. The arcuate sector, bisected by the spline yielding the smallest amplitude difference or the smallest phase difference, is selected. The bisection of the horizontal sector with the arcuate sector forms a pie shaped sector. The position of the ablation catheter in the pie shaped sector is determined according to the distance of the ablation catheter from the basket electrodes. The closer the ablation catheter is to the electrodes, the higher the peak voltage sensed from these electrodes. Thus, the distance from the electrodes is determined according to the sensed peak voltage during the determination of the arcuate sector.
U.S. Pat. No. 6,400,981 to Govari, entitled “Rapid Mapping of Electrical Activity in the Heart,” is directed to a method for mapping electrical potentials inside a volume. In Govari, a mapping catheter, including a plurality of electrodes is inserted into a chamber of the heart, to generate a map of the electrical activity over an endocardial surface of the heart. These electrodes are distributed over the surface of the distal part of the catheter. The catheter further includes at least one position sensor at the distal part of the catheter. A geometrical model of the endocardial surface is formed by the catheter. Electrical potentials are measured within the volume of the chamber using the electrodes on the catheter. Since the position of the electrodes with respect to the position sensor is known, the measured potentials are combined with the geometrical model, thus generating a map of the electrical potentials at the endocardial surface.